<h2>DESCRIPTION</h2>

<em>i.ifft</em> is an image processing program based on the algorithm given
by Frigo et al. (1998), that converts real and imaginary frequency space
images (produced by
<em><a href="i.fft.html">i.fft</a></em>) into a normal image.

<h2>NOTES</h2>

The current mask is respected when reading the real and imaginary 
component files;  thus, creating a mask is a primary step for selecting 
the portion of the frequency space data to be included in the inverse 
transform.  The module <em><a href="wxGUI.vdigit.html">wxGUI vector digitizer</a></em>
can be used to create masks while viewing the real 
or imaginary component image. Alternatively <em>r.circle</em> can be 
used to generate high-, low- and donut filters specifying the DC point 
as circle/ring center. When <em>i.ifft</em> is executed, it 
(automatically) uses the same GRASS region definition setting that was 
used during the original transformation done with
<em><a href="i.fft.html">i.fft</a></em>.


<h2>SEE ALSO</h2>

<em>
<a href="i.cca.html">i.cca</a>,
<a href="g.gui.iclass.html">g.gui.iclass</a>,
<a href="i.fft.html">i.fft</a>,
<a href="i.pca.html">i.pca</a>,
<a href="r.circle.html">r.circle</a>,
<a href="wxGUI.vdigit.html">wxGUI vector digitizer</a>
</em>

<h2>REFERENCES</h2>

<ul>
<li> M. Frigo and S. G. Johnson (1998): "FFTW: An Adaptive Software 
Architecture for the FFT". See <a href="http://www.fftw.org/">www.fftw.org</a>:
FFTW is a C subroutine library for computing the Discrete Fourier 
Transform (DFT) in one or more dimensions, of both real and complex 
data, and of arbitrary input size.</li>
<li> Richards, J.A (1986): <b>Remote Sensing Digital Image 
Analysis</b>, Springer-Verlag, 1986.</li>
<li> Personal communication, between program author and Ali R. Vali, 
Space Research Center, University of Texas, Austin, 1990.</li>
</ul>
	
<h2>AUTHORS</h2>

David Satnik, GIS Laboratory, 
Central Washington University
<br>
Glynn Clements (FFTW support)

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